PCR testing is expensive and, in most developing countries, available only through specialty laboratories. Because PCR testing is more complex than other common HIV laboratory assays (e.g. CD4+ cell counting), it requires technicians with considerably more training and technical skill, involves longer sample preparation time, and can be considerably more costly than other diagnostic tests. Thus, most countries with large populations of HIV-infected children have extremely limited capacity to carry out PCR testing. Even where PCR is available, pediatric HIV diagnosis may remain difficult in breastfeeding populations because infants are at continued risk of infection until breastfeeding is completely stopped. A negative PCR test during breastfeeding does not guarantee that the infant will remain uninfected. The alternative - serial testing for HIV infection - would result in an exponential increase in cost.